Systems Architecture -
• The CPU performs the FDE cycle (fetch, decode, execute)
- This is followed by a processor to process an instruction. The memory address held in the PC is
copied into the MAR. The address in the PC is then incremented by one, so now holds the address
of the next instruction.
- The processor sends a signal along the address bus to the memory address held in the MAR. The
instruction is sent along the data bus to the MDR. This is copied into the CIR. This is decoded and
executed. Results are stored in the ACC.
- The cycle then repeats back to step one.
• Factors that affects CPU performance:
- Clock speed: Sends out pulses in fixed intervals, measured in Hertz. Higher clock speed means
more FDE cycles per second.
- Cache size: Fast memory that stores frequently used instructions and data. Reduces time lost
whilst waiting to retrieve data from RAM.
- Number of cores: Number of processes that can happen at one time. Cores carry out FDE cycles,
more cores more instructions processed at one time. Only benefits in programs that can use multiple
cores. If lower clock speed but more cores, may still be faster.
• Components of a CPU:
- Control Unit (CU): Sends control signals around the CPU that control hardware.
- Registers: Small amounts of high speed memory that store data.
- Cache: Very fast memory that stores frequently used instructions so they don’t have to be fetched
(saves time).
- ALU (arithmetic logic unit): Performs calculations and logic checks.
• Registers:
- MAR (Memory Address Register): Holds address of current instruction to be fetched or to be
transferred.
- MDR (Memory Data Register): Holds contents found at address in the MAR, or data to be
transferred.
- PC (Program Counter): Holds memory address of next instruction to be fetched from primary
memory.
- ACC (Accumulator): Holds results of calculations from the ALU.
• An embedded system is a system built inside a larger device to perform a specific task. The
opposite is a general-purpose system such as a laptop (multiple purposes e.g. using the
internet). An example of an embedded system is a washing machine, drone, kettle, toaster, etc.
• Software licensing:
- Open source (e.g. Linux, Python): Program/application where the source code is available to the
public. It can be edited by users for their own purpose (a derivative) and is free, giving advertising
and a reputation. Many authors can contribute.
- Proprietary (e.g. Windows, Microsoft Office): Copyrighted software, can only be used with a paid
license (usually). The source code cannot be seen or modified. Usually free of bugs due to
, development (regular bug patches). Support available, updates/patches online information such as
video guides to use it.
• Primary storage:
- Primary storage stores programs and data currently in use. They are loaded from the disk to
primary storage.
- ROM (read-only memory) is a non-volatile memory (retained after power is turned off). It is stored
permanently and stores the BIOS (basic input output system) and boot-up sequence. BIOS has
instructions that load the OS from secondary storage to RAM.
- RAM (random access memory) temporarily stores data/programs/instructions currently in use by
the CPU. It is volatile meaning data is lost when the PC is turned off. It is much faster than
secondary storage so much more expensive.
• Secondary storage:
- Secondary storage is used for long-term storage of data/programs when not immediately needed.
It remains when the PC is turned off. Stores backups if original is damaged/destroyed.
- Magnetic (e.g. Hard drives, tapes, floppy disks): Large capacity for a low price. Reliable but not
robust due to moving parts. Slower R/W speeds.
- Solid state (e.g. SSDs, flash drives/USBs): Very fast speed, robust and portable (as no moving
parts), large capacity. However quite expensive.
- Optical storage (e.g. CDs, DVDs, blu-ray): Cheap and small capacity, low R/W speeds, unreliable
as prone to scratching.
- Factors to consider: Cost, capacity, speed, portability, durability, reliability.
• Units (denary, binary, hexadecimal):
- Bit, nibble (2 bits), bytes (8 bits), KB, MB, GB, TB, PB. Multiple or divide by 1000 to get between
each.
- Data needs to be in binary format to be understood by a computer as it works in on/off switches.
Transistors with two states.
- A shift multiplies or divides a number by 2. Shift left = x2. Shift right = /2.
- Hex: 10 = A, 11 = B, 12 = C, 13 = D, 14 = E, 15 = F.
• Characters:
- Each character is represented with a unique binary code.
- A character set is all of the characters that can be represented in a computer system.
- ASCII = 8 bits in character, 2^8 (256) possible characters.
- Unicode = 16 bits in character. 2^16 (65,536) possible characters. Enough to represent multiple
languages and emojis.
- Images are represented with pixels. The number of pixels is the resolution. The number of bits per
pixel is the colour depth.
- Metadata is data about data such as resolution, colour depth, file size, file type, author, height in
pixels, width in pixels.
- Larger colour depth = more bits per pixel = more possible colours = larger file size = better image
quality.
- Bitmap images are made up of individual pixels. For black and white it is just on and off (1 and 0),
however coloured imaged need additional binary code to store the colour. The more bits available to
• The CPU performs the FDE cycle (fetch, decode, execute)
- This is followed by a processor to process an instruction. The memory address held in the PC is
copied into the MAR. The address in the PC is then incremented by one, so now holds the address
of the next instruction.
- The processor sends a signal along the address bus to the memory address held in the MAR. The
instruction is sent along the data bus to the MDR. This is copied into the CIR. This is decoded and
executed. Results are stored in the ACC.
- The cycle then repeats back to step one.
• Factors that affects CPU performance:
- Clock speed: Sends out pulses in fixed intervals, measured in Hertz. Higher clock speed means
more FDE cycles per second.
- Cache size: Fast memory that stores frequently used instructions and data. Reduces time lost
whilst waiting to retrieve data from RAM.
- Number of cores: Number of processes that can happen at one time. Cores carry out FDE cycles,
more cores more instructions processed at one time. Only benefits in programs that can use multiple
cores. If lower clock speed but more cores, may still be faster.
• Components of a CPU:
- Control Unit (CU): Sends control signals around the CPU that control hardware.
- Registers: Small amounts of high speed memory that store data.
- Cache: Very fast memory that stores frequently used instructions so they don’t have to be fetched
(saves time).
- ALU (arithmetic logic unit): Performs calculations and logic checks.
• Registers:
- MAR (Memory Address Register): Holds address of current instruction to be fetched or to be
transferred.
- MDR (Memory Data Register): Holds contents found at address in the MAR, or data to be
transferred.
- PC (Program Counter): Holds memory address of next instruction to be fetched from primary
memory.
- ACC (Accumulator): Holds results of calculations from the ALU.
• An embedded system is a system built inside a larger device to perform a specific task. The
opposite is a general-purpose system such as a laptop (multiple purposes e.g. using the
internet). An example of an embedded system is a washing machine, drone, kettle, toaster, etc.
• Software licensing:
- Open source (e.g. Linux, Python): Program/application where the source code is available to the
public. It can be edited by users for their own purpose (a derivative) and is free, giving advertising
and a reputation. Many authors can contribute.
- Proprietary (e.g. Windows, Microsoft Office): Copyrighted software, can only be used with a paid
license (usually). The source code cannot be seen or modified. Usually free of bugs due to
, development (regular bug patches). Support available, updates/patches online information such as
video guides to use it.
• Primary storage:
- Primary storage stores programs and data currently in use. They are loaded from the disk to
primary storage.
- ROM (read-only memory) is a non-volatile memory (retained after power is turned off). It is stored
permanently and stores the BIOS (basic input output system) and boot-up sequence. BIOS has
instructions that load the OS from secondary storage to RAM.
- RAM (random access memory) temporarily stores data/programs/instructions currently in use by
the CPU. It is volatile meaning data is lost when the PC is turned off. It is much faster than
secondary storage so much more expensive.
• Secondary storage:
- Secondary storage is used for long-term storage of data/programs when not immediately needed.
It remains when the PC is turned off. Stores backups if original is damaged/destroyed.
- Magnetic (e.g. Hard drives, tapes, floppy disks): Large capacity for a low price. Reliable but not
robust due to moving parts. Slower R/W speeds.
- Solid state (e.g. SSDs, flash drives/USBs): Very fast speed, robust and portable (as no moving
parts), large capacity. However quite expensive.
- Optical storage (e.g. CDs, DVDs, blu-ray): Cheap and small capacity, low R/W speeds, unreliable
as prone to scratching.
- Factors to consider: Cost, capacity, speed, portability, durability, reliability.
• Units (denary, binary, hexadecimal):
- Bit, nibble (2 bits), bytes (8 bits), KB, MB, GB, TB, PB. Multiple or divide by 1000 to get between
each.
- Data needs to be in binary format to be understood by a computer as it works in on/off switches.
Transistors with two states.
- A shift multiplies or divides a number by 2. Shift left = x2. Shift right = /2.
- Hex: 10 = A, 11 = B, 12 = C, 13 = D, 14 = E, 15 = F.
• Characters:
- Each character is represented with a unique binary code.
- A character set is all of the characters that can be represented in a computer system.
- ASCII = 8 bits in character, 2^8 (256) possible characters.
- Unicode = 16 bits in character. 2^16 (65,536) possible characters. Enough to represent multiple
languages and emojis.
- Images are represented with pixels. The number of pixels is the resolution. The number of bits per
pixel is the colour depth.
- Metadata is data about data such as resolution, colour depth, file size, file type, author, height in
pixels, width in pixels.
- Larger colour depth = more bits per pixel = more possible colours = larger file size = better image
quality.
- Bitmap images are made up of individual pixels. For black and white it is just on and off (1 and 0),
however coloured imaged need additional binary code to store the colour. The more bits available to
